TWO RECORD-BREAKING BLACK HOLES FOUND HIDING NEARBY

December 1, 2011

Figure 1. Artist's conceptualization of the stellar environment around a black hole of about 10 billion solar masses. The velocity of stars in orbit (and close to) the black hole help to determine its mass. Gemini Observatory/AURA illustration by Lynette Cook.

Figure 2. This picture illustrates the immense size of the black holes discovered. The black holes reside at the centers of the two galaxies, each of which is the brightest galaxies in a cluster of galaxies. The background image shows the brightest galaxy in the cluster Abell 1367, which host one of the black holes. The event horizons are several times larger than Pluto's orbit. Our solar system would be dwarfed by the holes. P. Marenfeld/NOAO/AURA/NSF

Observations with the
Gemini North telescope in Hawai‘i reveal evidence for
what astronomers are calling the largest black holes ever measured in our
nearby cosmological neighborhood. This result is crucial in explaining the
long-standing mystery of where the largest black holes are hiding in our
present-day universe.

Supermassive black holes
appear to have existed when the universe was extremely young. Evidence for this
comes from quasars – extremely bright objects
thought to have played host to very massive black holes in the early universe.

"They couldn't just
go away," says University of California at Berkeley graduate student
Nicholas McConnell, who is first author of a paper in the December 8, 2011
issue of the journal Nature. "So
where are these black holes hiding now?" McConnell asks.

The discovery of these
two supermassive black holes, each approaching 10 billion times the mass of the
Sun, is providing answers to this question.

At this stage, it's too early to tell
whether these two black holes are a rare find or just the tip of the iceberg, says McConnell. In the next few years, we plan to examine a dozen or more of the largest galaxies in the local universe to look
for more black holes of similar masses. Finding more will confirm that the
universe once contained prime real estate for growing giant black holes.

McConnell and his advisor and team-leader Chung-Pei Ma were
joined by researchers from the universities of Texas, Michigan, the Dunlap
Institute for Astronomy and Astrophysics at the University of Toronto, Canada,
as well as the National Optical Astronomy Observatory (NOAO) in Arizona.

“The
boisterous quasars that we see when we look back in time at the young universe
may have passed through a turbulent youth to become the quiescent giant
elliptical galaxies we see today,” says Ma. “The
black holes at the centers of these galaxies are no longer fed by accreting gas
and have become dormant and hidden. We see them only because of their
gravitational pull on nearby orbiting stars. ”The question remains whether there
is a limit as to how big a black hole can get. “Larger black holes tend to live in
bigger parent galaxies so,” Ma continues, “is it nature or nurture that determines how large a black hole can grow?"

In addition to the Gemini observations, follow-up data from
the W.M. Keck and McDonald observatories supported the team’s conclusion that these black holes
are record-holders. “We
believe that 10-billion solar mass black holes like these are the ultimate
power sources for the distant quasars observed in the early universe, one to
three billion years after the Big Bang,” says James Graham of the Canadian Dunlap Institute. A video interview with
Graham and McConnell is available at: http://vimeo.com/32575164 – pw: 2011December08.

The astronomers found the black holes in NGC 3842 and NGC
4889: each a giant elliptical galaxy and the brightest member of a galaxy
cluster; NGC 3842 lies about 320 million light-years away in the Leo galaxy
cluster, and NGC 4889 is the brightest member of the famous Coma galaxy cluster
some 336 million light-years distant. Both of these galaxies are bright enough
to spot in amateur telescopes.

McConnell adds that while the galaxies studied are
relatively close, it
is extremely difficult to observe the stars within about 1000 light-years of
the black hole at a distance of about 300 million light-years. Only stars
orbiting in this small region surrounding the black hole are sensitive enough
to the hole's gravity to be used to determine its mass. "This means we
need exquisite observing conditions and the latest technology to have any hope
of seeing what's going on around the black hole," McConnell explains.

The two black holes discovered in this research are more
than two thousand times bigger than the one that resides at the center of our
Galaxy, which has a mass of about 4 million times that of our Sun. Team member
Tod R. Lauer of NOAO notes that the event horizons (the region inside of which
light can no longer escape) of these black holes are far larger than our Solar
System. Each is five to ten times bigger than Pluto's orbit.

The previous entry into the most massive black hole race
was led by Karl Gebhardt from the University of Texas Austin (also on the
research team making this discovery). At the American Astronomical Society
meeting in January 2011, he reported that the black hole in the giant
elliptical galaxy M87 was 6.3 billion times the mass of our Sun (see Gemini
press release at: /node/11588). "They just keep
getting bigger!”
says Gebhardt. “My
record holder in M87 is now dwarfed by about a factor of two by both of these
new discoveries. It's all very exciting!"

Other coauthors of the Nature
paper are Hubble postdoctoral fellow Shelley A. Wright at the University of
California at Berkeley and graduate student Jeremy D. Murphy of the University
of Texas; and Douglas O. Richstone of the University of Michigan in Ann Arbor.

The research was supported by the National Science
Foundation, the National Aeronautics and Space Administration, and UC Berkeley's Miller Institute for Basic Research
in Science.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Maunakea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in five partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, the Brazilian Ministério da Ciência, Tecnologia e Inovação and the Chilean Comisión Nacional de Investigación Científica y Tecnológica (CONICYT). The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.